The goal of this project is to identify and characterize B lymphocyte receptors for lymphokines via the production of monoclonal antibodies. One promising Mab (F1-10) has been obtained so far. This antibody binds to LPS stimulated B lympho-blasts and some B cell tumors. Minimal binding is seen with a minority of normal B cells and bone marrow cells. Peripheral T lymphocytes, thymocytes, and concanavalin A stimulated T lymphoblasts are negative. Time course experiments reveal that expression of the F1-10 antigen peaks 60 hours after stimulation with LPS and the kinetics of expression is distinct from other B lymphocyte membrane molecules. Strain distribution studies reveal that expression of the F1-10 antigen is linked to H-2 in that DBA/2 (prototypic strain) and B10.D2 are positive while B10 is negative. However, control of expression is complex in that other strains which are haplotype identical to DBA/2 in one or several of the H-2 regions (K,I,D,T1A) are negative. These data suggest that F1-10 is recognizing a previously undescribed B lymphocyte membrane molecule and are consistent with the possibility that this molecule is a lymphokine receptor.